This invention relates to a recording and/or reproducing apparatus of the type which uses a rotating recording medium such as a rotating magnetic sheet or disc. More particularly, the invention relates to an apparatus wherein one head moves over a rotating recording medium within a vertical blanking period of a video signal. A video signal of one field or one frame is recorded and reproduced on each circular track of the medium.
The applicant has previously proposed apparatus a plurality of magnetic heads, for example, two, are alternately and stepwise over a rotating recording medium, such as a rotating magnetic sheet or a rotating magnetic disc. Movement is in the radial direction across the disc to record or reproduce video signals. In this apparatus, each magnetic head intermittently steps over two track pitches at a time and steps over one track pitch only at the time when there is a reversal of the direction of stepping. Thus, the forward path track and the return path track are formed alternately. During each of its stopped periods, each magnetic head records or reproduces one field or one frame of a video signal on the rotating recording medium.
Since two channel heads are used in this previously proposed apparatus, two head systems including driving means for each head are necessary. Therefore, the proposed apparatus had the disadvantages of complexity and high cost.
On one hand, a so-called field-skip recording system, wherein only one head system. The signal of only the odd-number or even-number fields of one frame is recorded in every other fields, has also been proposed. By this system, however, a so-called full-field recording, wherein all fields are recorded, cannot be carried out.
Furthermore, in order to cause a magnetic head to step by two track pitches (in an ordinary forward path or return path) and by one track pitch (at the time of reversal of stepwise advance direction), it has heretofore been the practice to use a pulse motor as a step driving power source. For the applied pulse, two pulses or four pulses are used at the time of 2-track pitch stepping, and one pulse or two pulses at the time of 1-track pitch stepping. Because of the changing of the number of applied pulses in this manner, the circuit for controlling the applied pulses becomes complicated. Moreover, stepping cannot be carried out at high speed.
Accordingly, in order to simplify the organization of the apparatus, it is desirable to use only one head system. Furthermore, in order to record and reproduce video signals of all fields with a magnetic head of one channel, it is necessary to cause the magnetic head to step at high speed within a vertical blanking period because there is substantially no video information at that time. For this purpose, it is desirable that constant pulses be applied to the pulse motor as the head driving power source for both ordinary the stepping and reversal of stepping direction. Furthermore, since the vertical synchronizing signal is not recorded very well at the time of recording, it is necessary to artificially compensate for this loss of vertical synchronizing signal, at the time of reproducing.